What is the ruling on the prayer of one who prayed while in a state of major ritual impurity (janabah)? Is that considered mockery of the religion? And does it annul the marriage contract?

You are obliged to repent, and you do not become a disbeliever by that according to the majority of scholars, nor is your marriage annulled. You were correct in performing that prayer. There is no evidence to disbelieve someone who tried to make people believe he was saying "Ameen," nor is there evidence that his heart expanded with disbelief. So, ward off these whispers and engage in repentance. Do not let shyness from people prevent you from performing the obligatory purification for prayer, and do not repeat that action again. For a slave was lashed one hundred times in his grave, which became a single lash, yet his grave became filled with fire because he prayed without purification and passed by an oppressed person but did not help him.